Linear polyethylene stabilized with alkali phosphates



United States Patent LINEAR POLYETHYLENE STABILIZED WITH ALKALI PHOSPHATES Charles R. Pfeifer and Mark R. Kinter, Midland, Mich., assignors to The Dow Chemical Company, Midland,

Mich., a corporation of Delaware '..No Drawing. Filed Dec. 19, 1955, Ser. No. 553,722

'11 Claims. (Cl. 26045.7)

This invention relates to improved, non-corrosive compositions comprised of select corrosion-inhibiting agents andpolymerized olefinic and other ethylenically unsaturated materials which have been prepared with certain catalytic metal compounds. In particular it relates to compositions of this nature which are not corrosive to metals and other materials of construction, particularly ferrous metals and alloys that do not have special corrosion-resisting properties and that are susceptible to attack from hydrogen halides and like corrodents, especially at elevated temperatures. The invention also relates to a method for preparing such compositions.

Various olefins and other ethylenically unsaturated materials, particularly ethylene, may be efiiciently polymerized, even as relatively impure materials, to high molecular weight polymeric compounds at comparatively low pressures and temperatures, according to a process.

first proposed by Karl Ziegler and his associates in Ger? many. In this process, mixtures of strong reducing agents such as aluminum alkyls with compounds of group IV-B, V-B, and VI-B metals of the periodic system including thorium and uranium are employed as catalysts for the polymerization. Polyethylenes, for example, havmg average apparent molecular weights (as indicated by measurement of such characteristics as their melt viscosities and the like) in excess of 40,000 and as large as 100,000 to 3,000,000 can be manufactured by polymerizing ethylene gas with such catalysts at temperatures beneath about 100 C. and under pressures less than about 100 atmospheres. It is frequently preferable when employing such catalysts according to the Ziegler process to'operate at temperatures of about 50 C. and under pressures between about 1 and atmospheres. The reaction may suitably be conducted in the presence of an organic liquid medium such as hexane, benzene, saturated petroleum hydrocarbon fractions and the like.

The polyethylenes prepared by the Zeigler process have superior and highly desirable properties. For example, they may be made containing less than 3 and even less than 0.03 methyl groups per each 100 methylene groups in the polymer molecule. The polymer molecules are practically completely linear and are crystalline almost to their melting points, which usually are in the neighborhood of about 125l35 C. Their densities are commonly in the range of about 0.94-0.96 gram per cubic centimeter. and higher. They are insoluble in most solvents at ordinary temperatures. Shaped articles formed with such polyethylenes have tear strengths between about 1,400 and 2800 pounds per square inch. Unstretched films prepared from them have tensile strengths in excess of about 2800 pounds per square inch and may be oriented by stretching to polyethylene film structures having tensile strengths as high as about 42,500 pounds per square inch.

The strong reducing agents which advantageously are employed in the catalyst mixtures of the Ziegler process include, among other compounds, a variety of aluminum trialkyls such as aluminum trimethyl, aluminum triethyl,

aluminum tripropyl, aluminum triisobutyl and higher aluminum trialkyls as well as dialkyl aluminum halides, dialkyl aluminum hydrides and dialkyl aluminum alkoxides.

Salts of metals selected from the group consisting of titanium, zirconium, uranium, thorium and chromium are preferably employed as the group IV-B, VB, and VI-B metallic compounds in the catalyst, although salts of the remaining metals in these sub-groups may also be employed. Compounds of these metals including their halogenides, oxyhalogenides, complex halogenides, freshly precipitated oxides and hydroxides and such organic compounds as alcoholates, acetates, benzoates, acetyl acetonates and the like may be used in the catalyst.

A particularly active catalyst mixture for the Ziegler process may be obtained by mixing a titanium or zirconium compound, such as a tetrachloride, oxychloride or acetyl acetonate with an aluminum trialkyl or a dialkyl aluminum compound. Generally, the molar quan tities of the aluminum alkyl employed to constitute the catalyst admixture are two to three times the valence of the group IV-B, V-B, and VI-B metal compound for each mole of the latter compound which is present, although many other ratios may also be employed satisfactorily. Amounts of the catalyst admixture varying from 0.01 to a few percent by weight, depending on the degree of purity of the materials being polymerized, the desired rate of polymerization and the intended molecular weight, may suitably be employed.

After polymerization according to the Ziegler process, however, polyethylene and similar polymerized products contain residues from the admixed metallic catalyst employed. The residues are not sufiiciently removed by the conventionally utilized aftertreatment of polymeric materials prepared according to the Ziegler process. Such aftertreatment usually involves filtration, preferably in the presence of air (which tends to lighten the color of the product), to separate the polymerization product from the reaction mass. This may be followed by sequential trituration with hexane, isopropanol, water, acetone and pentane prior to drying. When higher catalyst concentrations are employed in the Ziegler process, some of the metallic compounds may be removed from the polymeric product by extracting it with methanolic hydrochloric acid, then washing it in methanol or acetone. Butanol washings after the filtration in air have also been proposed to decompose and remove the catalyst 3 residue.

It has been observed that the presence of certain catalyst residues in polymeric materials prepared according to the Ziegler process tends to impart decidedly undesirable characteristics to the polymers. For example,

such polymers, particularly when the catalyst residue contains halogens, especially chlorine, which may cause hydrogen halides in the presence or absence of moisture,

particularly hydrogen chloride. Many of the frequently employed ferrous metals and alloys are susceptible to such corrosive attack, especially at elevated temperatures.

While various substances have been employed in other halogen-containing polymeric materials to diminish their corrosive propensities by counterefiecting the presence of or acting as receptors for hydrogen halides and the like which may be present or formed in the polymer, many of these substances are not well suited for employment with polymeric materials, particularly polyethylene; The reason,

prepared according to the Ziegler process.

Patented Sept. 13, 1960 forthis is that a considerable proportion of the conventionally available substances tend to decompose or become ineifective at the relatively high temperatures which are beneficially employed. for, fabricating Ziegler-l type polymericmaterials;particularly polyethylene. Fab} ricating temperatures in excess of about 200,?" Ca and frequently as high as 300 to.350 C. havebeenfound advantageous for fabricating such polymers as polyethylene. prepared according to theZiegler. process. 111 order to obtain optimum physical properties in the. fabricated polymeric article. In addition, many of the conventional corrosion-inhibiting substances tendto be toxic,

This, further lessens the desirability oftheir being em-.

ployed' in articles intended for association with foodstuifs. such as films, containers, cartons and thelike.

It would be advantageous, therefore, to.provide compositions prepared with halogen-containing catalyst admixtures according to the Ziegler process. andfcontaining.

sides being non-corrosive, many such compositions were non-toxic and adapted, for employment in articles intended for association withfoodstuifs or in other appli cations wherein appreciable toxicity couldfnot be tolerated. Q r a V These and other advantages and benefits may be realized according to the compositions provided by the present: invention which are comprised of a polymerized olefinic, and other ethylenically unsaturated material, particularly polyethylene, prepared with halogen containing catalyst according to the herein described Ziegler process and containing halogen-including'residues from thecatalyst which tend to cause the presence, of a hydrogen halide, particularly hydrogen chloride, orlike corrodent in the polymerized substance-and a corrosion-inhibiting quantity of a salt compound of an organic phosphonic acid and a metal from the first two. groups of the periodic system which has a receptor function for and is capable of: counterefiecting hydrogen halide and like corrodents; The compounds are members of the class of compounds which may be represented by either of the formulas M RPO or NRPO depending on the valence. of the metal constituent, wherein M represents a group I metal, N. represents a group II metal and R is anorganic radical which may be of the alkyl, aryl or aryl-alkyl type. Ordinarily, the organic phosphonic acid salt compound may advantageously be employed inthe composition in an amount between about 0.005 and 5 percent by weight, based on the Weight of the composition. Frequently, in order to satisfactorily inhibit the corrosive nature of many of the polymeric materials prepared according to the Ziegler process, an amount between about 0.5 and 2.0 percent by weight, based on the weight of the composition. may be utilized; of the organic phosphonic acid salt compound which will suitably inhibit corrosion can be predicated on the rela tive proportion of the halogen-including catalyst residue which remains in the polymer product and the degree of the residues tendency to cause the presence of a corrodent therein. Consideration of these factors under the influence of elevatedtemperatures must also be involved whenever fabrication of the corrosion-inhibited polymer;

fabrication, even when such apparatus is constructed from such materials as mild steel and'other frequently utilized ferrous metals and alloys having poor resistance to. corrosion from hydrogen halides, particularly hydroe' gen, chloride, and, like corrodents, 'Ihe inhibition. of cor- In all cases the relative amount,

' a large proportion of the compositions are non-toxic and rosion of the apparatus is also advantageously obtained during fabrications at elevated temperatures. The compositions do not necessitate employing fabricating apparatus which is made from relatively more expensive materials of construction which have special corrosionresisting characteristics and. eliminate the expensive damage and waste which occurs when conventional apparatus is corroded. In addition, better quality productsmay be obtained when the fabricating apparatusis kept free from the physical damage caused by corrosion. Furthermore,

may be employed safely with foodstuffs. In addition, many of the corrosion-inhibitors according to the present invention enhance certain other of the properties 'of the compositions, as for example, appearance, which may frequently be benefited by incorporation of a corrosion inhibitor having an ancillary pigmentation effect. Also, the great majority of the compositions. of the present invention are tolerant of the presence of other conventional additament materialswhich may be employed if required for such various purposes asto stabilize thecomposition against the effects of heat or. light, or oxygen toimpart' color or to attain other specific'and desirable benefits.

Compounds selected from the organic phosphonic acid salts of the group I and II metals of h periodic system.

may advantageously be employedgas,corrosioninhibitors in compositionsaccording to the present inventionwith particular advantages being derivable, when the metals are'the alkali Or alkalinejearth metals and the organic phosphonic acid is an alkyl or, aryl phosphonic acid. i

Greater advantages may frequently, accrue when. alkali metal and alkaline earth metal salts of benzenephosphonic acid or derivatives thereof are employed,

In a series of illustrative examples various corrosioninhibiting compounds were incorporated in a relatively.

high molecular weight polyethylene which was prepared with an admixed aluminum alkyl-titanium tetrachloride catalyst according to the herein described Ziegler process" and contained between about 70.02 and 0.08.percen t. weight based on the weight of the polyethylene, of chloride in the catalyst, residue. In each of the tests a small plate of mild steel (1" x 1" x /3 having a finished surface was imbedded under compression molding within a particular polyethylene, sample in order to. form a steelin-polymer matrix. Each of the test matrices wasthen'.

maintained at a temperature of about 250? C. for. about twelve hours after which it was. cooled and stripped of the polymer. Each of the test plates was permitted to remain overnight in air before being examined. The

test plates were then inspected for evidences of corrosion,-

The following table reproduces the results obtainedwith several corrosion-inhibiting compounds.

Similar excellent results may be obtained such corrosion-inhibiting additament materials as laurylphosphonateand disodium octylphosphonate The. corrosion-inhibiting compounds may be incorpo:

rated in compositions according to the. present invention in various suitable ways, including dryrblending' the in gredients; mixing the ingredients jon compounding rolls and the like; and dispersing the corrosion-inhibiting coinpound from liquid dispersion ontothe polymer particles followed by evaporation of the liquid.

Since certain changes andmodifications nihq Practice girlie n eseat v ntiga an ntered n read l w th out departing substantially from its intended spirit and scope, it is to be fully understood that all of the foregoing description and specification be interpreted as merely being descriptive of certain of its preferred embodiments and not construed as being limiting or restrictive of the invention excepting as it is set forth and defined in the appended claims.

What is claimed is:

l. A non-corrosive composition comprising polyethylene prepared by polymerizing ethylene in the presence of a halogen-containing catalyst formed by admixing an aluminum alkyl with a titanium halide, said polyethylene containing halogen-including catalyst residues after having been polymerized which cause the presence of hydrogen halide in the polymerized material, and between about 0.005 percent and 5 percent by weight of a corrosioninhibiting salt compound which has a receptor function for and is capable of counter-effecting hydrogen halide, said corrosion-inhibiting compound being selected from the group consisting of disodium benzenephosphonate, disodium octylphosphonate, dipotassium benzenephosphonate, calcium benzenephosphonate, zinc benzenephosphonate, and calcium laurylphosphonate.

2. A composition of claim 1 containing between about 0.5 and 2.0 percent by weight of the corrosion-inhibiting compound.

3. The composition of claim 1 wherein the corrosion inhibitor is disodium benzenephosphonate.

4. The composition of claim 1 wherein the corrosion inhibitor is dipotassium benzenephosphonate.

5. The composition of claim 1 wherein the corrosion inhibitor is calcium benzenephosphonate.

6. The composition of claim 1 wherein the corrosion inhibitor is zinc benzenephosphonate.

7. The composition of claim 1 wherein the polyethylene is prepared by polymerizing ethylene in the presence of a catalyst formed by admixing an aluminum alkyl with titanium tetrachloride.

8. The composition of claim 1 characterized in being non-corrosive to materials susceptible to attack from 40 hydrogen halides at temperatures up to about 350 C. 9. The composition of claim 1 characterized in being non-corrosive to mild steel at fabricating temperatures for the composition.

10. A non-corrosive composition comprising polyethylene prepared by polymerizing ethylene in the presence 5 of a halogen-containing catalyst formed by admixing (1) an aluminum alkyl and (2) a compound selected from the group consisting of halogenides, oxyhalogenides, complex halogenides, freshly precipitated hydroxides, alcoholates, acetates, benzoates, and acetyl acetonates of a metal selected from the group consisting of titanium, zirconium, uranium, thorium, and chromium, said polyethylene containing halogen-including catalyst residues after having been polymerized which cause the presence of hydrogen halide in the polymerized material, and between about 0.005 percent and 5 percent by weight of a corrosion-inhibiting salt compound which has a receptor function for and is capable of counter-effecting hydrogen halide, said corrosion-inhibiting compound being selected from the group consisting of disodium benzenephosphonate, disodium octylphosphonate, dipotassium benzenephosphonate, calcium benzenephosphonate, zinc benzenephosphonate, and calcium laurylphosphonate.

11. The composition of claim containing between about 0.5 and 2.0 percent by weight of the corrosioninhibiting compound.

References Cited in the file of this patent UNITED STATES PATENTS Chaban May 9, 1950 Linville Mar. 27, 1956 Friedlander July 15, 1958 FOREIGN PATENTS Belgium May 16, 1955 OTHER REFERENCES Pauling: General Chemistry, copyright 1947, published by W. H. Freeman & Co., inside cover.

Partington: Text-Book of Inorganic Chemistry, reprinted 1953, pub. Macmillan & Co., London, pages 367 and 368. 

1. A NON-CORROSIVE COMPOSITION COMPRISING POLYETHYLENE PREPARED BY POLYMERIZING ETHYLENE IN THE PRESENCE OF A HALOGEN-CONTAINING CATALYST FORMED BY ADMIXING AN ALUMINUM ALKYL WITH A TITANIUM HALIDE, SAID POLYMETHYLENE CONTAINING HALOGEN-INCLUDING CATALYST RESIDUES AFTER HAVING BEEN POLYMERIZED WHICH CAUSE THE PRESENCE OF HYDROGEN HALIDE IN THE POLYMERIZED MATERIAL, AND BETWEEN ABOUT 0.005 PERCENT AND 5 PERCENT BY WEIGHT OF A CORROSIONINHIBITING SALT COMPOUND WHICH HAS A RECEPTOR FUNCTION FOR AND IS CAPABLE OF COUNTER-EFFECTING HYDROGEN HALIDE, SAID CORROSION-INHIBITING COMPOUND BEING SELECTED FROM THE GROUP CONSISTING OF DISODIUM BENEZENEPHOSPHONATE, DISODIUM OCTYLPHOSPHONATE, DIPOTASSIUM BENZENEPHOSPHONATE, CALCIUM BENZENEPHOSPHONATE, ZINC BENZENEPHOSPHONATE, AND CALCIUM LAURYLPHOSPHONATE. 